Plural motor slip-controlled driving means for traction purposes

ABSTRACT

A slip controlled driving means for traction purposes includes a plurality of direct current motors connected to various wheel shafts. They are provided with control rectifiers forming valve control systems to control the motor current. The rectifiers respond to a first reference value supplied to the system by a first reference value transducer, a current transducer for the rotor current and a tachometer for each motor. A minimum selector is provided to compare the output values of all the tachometers and to pick out the lowest one. A reference value transducer can be set for the permissible difference between a certain motor speed and the speed of the motor rotating at the lowest speed. A summation device produces the sum of the lowest tachometer value and this difference reference, and a plurality of comparison devices are each connected to a tachometer and arranged to produce the positive difference between the output value of one tachometer and such sum. This positive difference is supplied to each of the control systems in such a way as to reduce the driving current of the motor.

llnited States Patent 1 Hermansson et al.

[ 51 Apr. 17, 1973 PLURAL MOTOR SLIP-CONTROLLED DRIVING MEANS FOR TRACTION PURPOSES [75] Inventors: B0 Hermansson; Jorgen Gustafsson,

both of Vasteras, Sweden [73] Assignee: Allmanna Svenska Elektriska Aktiebolaget, Vasteras, Sweden 22 Filed: Mar.8, 1971 21 Appl.No.: 121,977

UNITED STATES PATENTS 3,210,630 l0/l965 Zelina ..3l8/52 3,577,048 5/1971 Nordin ..3l8/52 2,652,555 9/1953 Smith ..3l8/52 X Primary Examiner-T. E. Lynch Attorney-Jennings Bailey, Jr.

[57] ABSTRACT A slip controlled driving means for traction purposes includes a plurality of direct current motors connected to various wheel shafts. They are provided with control rectifiers forming valve control systems to control the motor current. The rectifiers respond to a first reference value supplied to the system by a first reference value transducer, a current transducer for the rotor current and a tachometer for each motor. A minimum selector is provided to compare the output values of all the tachometers and to pick out the lowest one. A reference value transducer can be set for the permissible difference between a certain motor speed and the speed of the motor rotating at the lowest speed. A summation device produces the sum of the lowest tachometer value and this difference reference, and a plurality of comparison devices are each connected to a tachometer and arranged to produce the positive difference between the output value of one tachometer and such sum. This positive difference is supplied to each of the control systems in such a way as to reduce the driving current of the mo- I01.

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' SHEET BF 5 IN VENT OR PLURAL MOTOR SLIP-CONTROLLED DRIVING MEANS FOR TRACTION PURPOSES BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a slip-controlled driving means for traction purposes comprising a plurality of direct current motors connected to various wheel shafts, the motors together with the controlled rectifiers comprising individual control systems to control the motor current in dependence on a first reference value supplied to the system by means of a first reference-value transducer, a current transducer for the rotor current and a tachometer being arranged for each motor.

2. The Prior Art In, for example, driving systems for locomotives where the driving is carried out by a plurality of motors connected to various wheel shafts, it is desirable to distribute the load equally between the motors in order to use the equipment to its fullest advantage.

U.S. Pat. application Ser. No. 787,182, filed Dec. 26, 1968 describes such a driving system comprising a plurality of separately excited motors connected in parallel, uniform load distribution being achieved by means of a control system which, within certain limits, reduces the field of the motors which tend to carry too little load. The known device aims especially at counteracting the inconveniences which arise when there are differences in wheel diameter and/or motors.

SUMMARY OF THE INVENTION The present invention is an improvement of the above-mentioned system in that the fact is taken into consideration that considerable differences in adhesion conditions may arise at the various wheels. When this occurs the regulating system of the known device reacts by increasing the speed ofa motor having poorer adhesion, which is done by a reduction of the excitation current of this motor.

FIG. 1 of the accompanying drawings shows an example of adhesion curves for two wheels for example on a locomotive. Curve A corresponds to a wheel having relatively good adhesion and curve B to a wheel with poorer adhesion. Each curve shows the transferable torque M as a function of the over-speed A n. The over-speed A n is defined as the difference between the speed of a wheel and the speed the wheel would have had at the same speed of the locomotive if slipping had been equal to zero.

In the known device the control is carried out in such a way that load points belonging together lie on a horizontal line. This means that maximum adhesion of the wheel pair operating with poorest adhesion also provides the upper limit of useful adhesion of the wheel pair having better adhesion.

An important improvement is achieved with a driving means according to the invention in comparison with similar known driving means. The means is characterized in that it includes a minimum selector which is arranged to compare the output values of all the tachometers and pick out the lowest of these, a reference-value transducer to set the permissible difference between a certain motor speed and the speed of the motor rotating at the slowest speed, a summation device to produce the sum of said lowest tachometer value and said difference reference, and a plurality of comparison devices, each connected to a tachometer and arranged to produce the positive difference between the output value of one tachometer and said sum, whereupon such positive differences are supplied to each of said first control systems with a reducing action on said first reference value.

BRIEF DESCRIPTION OF THE DRAWINGS In the following the invention will be described with reference to the accompanying drawings in which FIG. 1 shows adhesion curves;

FIG. 2 shows one embodiment of the invention;

FIGS. 2a and 2b show details of FIG. 2;

FIG. 3 shows another modification of the invention;

FIGS. 3a and 3b show details of FIG. 3; and

FIG 4 shows a minimum selector.

The device shown in FIG. 2 is individually controlled in the rotor circuits of the motors and that shown in FIG. 3 has individual control of the field currents of the motors.

In FIG. 2, l designates direct current motors. The motors receive armature current from individual controlled rectifiers 10 connected to a network not shown in the drawing, each rectifier constituting, together with an amplifier 12, forming a comparison device 13 and a transducer 3, a part of a closed control system to regulate the motor current. The motors l are provided with individual tachometer-generators 4 and these are connected to the minimum value selector 5 which picks out the signal from the motor rotating most slowly and gives this to the summation device 7 and comparison device 14, which also receive the output values from the reference value transducers 6 and 2, respectively. 15, 16 and 17 are amplifiers intended for amplification of the output values from the devices 7, 8 and 14.

During normal operation, when thereis no noticeable over-speed, the reference. value to the device 13 is delivered only from the amplifier 17, which means that the motors divide the load equally. If thelimit for transferrable torque is then approached, motors having different adhesion ability .tend to deviate from each other in speed. The greatest permissible difference between the speed of one motor and that of the slowest rotating motor is set on the difference value transducer 6. As long as the sum of the output value from the device 5 and the output value from the device 6 or the amplification by the amplifier 15 is greater than any tachometer signal supplied from any of the motors to a device 8, the output magnitude from the-amplifier 16 is equal to zero, but, when the motor runs so fast that the above relation ceases, the amplifier l6 delivers an output value which is supplied to the device 13 where it counteracts the reference value delivered by the amplifier 17, which means a reduction of the desired value for the rotor current of the corresponding motor, and such a great reduction of the slipping of the wheel pair operating with lowest adhesion, therefore, that the difference between the highest and lowest motor speed lies below the permissible value. v

If the line marked with arrows S in FIG. 1 corresponds to the permissible difference mentioned above and A and B are the adhesion curves for the two motors in FIG. 2, it is seen that uniform load-distribution is obtained as long as the motor torque is below M If, while maintaining the value S, a higher torque value is set (with the help of the reference value transducer 2 in the embodiment shown in FIG. 2 or with the help of the device 9 shown in FIG. 3), the total torque transmitted is increased in such a way that the slipping increase required is distributed relatively uniformly between the two motors. This gives advantages from the point of view of wear and also in the form of reduced risk of racing.

Whereas the points on the curves A and B which are characteristic for a certain operating condition of the vehicle lie substantially on a horizontal line with the known driving means mentioned above, with a driving means according to the invention these points are in an almost vertical line. (For example points P P in FIG. 1.) Thus, with a device according to the invention, even with different adhesion ability for the different wheel pairs, the transferrable torque for the whole vehicle will be almost equal to the sum of the maximum transferrable torque of the different wheel pairs.

If there is a sudden drop in the curveB, for example during the operating conditions characterized by the points P and P this means that the difference in speed will suddenly be greater than S1 and the current desired value for the most rapidly rotating motor is therefore reduced. The regulator equipment of the driving system is thus also an effective protection against racing.

The driving means shown in FIG. 2 can also be constructed with separately excited motors. In the means shown in FIG. 3 the motors receive their energy supply from a common rectifier connected to a network not shown in the drawing, for example a controlled rectifier 20. The designations l, 3, 4, 5, 6, 7, 8,15 have the same meaning as in FIG. 2. Each motor 1 is provided with a separately excited fieldwinding 1s. The field winding is fed by a converter 10a connected to-the network, and controlled by a regulator including an amplifier 21. The amplifier 21 is connected by its input side to the difference device 22 which is arranged to be supplied with an actual value from a field current transducer 11. The reference value of the field current is composed of the output value from the reference value transducer 9 and the output value from the amplifier 23, the input side of which is supplied with the difference between an actual value from the rotor current transducer 3 and a value corresponding to the difference between the greatest rotor current and the maximum permitted rotor current difference, the latter being set by means of the difference reference device 29. The greatest rotor current, that is the rotor current of the most heavily loaded motor, is selected by means of a maximum value selector 25 and supplied to a difference device 27 connected to an amplifier 26. The output value from the amplifier 26'is compared in the device 24 with a value which corresponds to the rotor current of the motor in question and, if the rotor current of the motor is lower than permitted, the amplifier 23 is activated in such a way that the output magnitude delivered to the device 22 counteracts the reference value delivered by the reference value emitter 9, which means that the excitation current in the field winding 1,, is reduced until the desired load-distribution is obtained. The amplifier 23 (as is clear from the static characteristic drawn in in graphic symbol) is normally limited so that it cannot increase the field current. While the combination of a device 23 and a device 24 provides a load-regulator, a difference device 8 in combination with an amplifier 28 provides a slipping regulator. If the difference expressed by the device 8 between the speed of a motor and the motor speed (expressed as a tachometer signal) picked out by the minimum value selector 5 is less than a value set by the potentiometer 6, the output magnitude from the amplifier 28 will be equal to zero. On the other hand, if the speed of one motor exceeds the speed of the slowest rotating machine more than is permitted by the potentiometer 6, the slipping regulator (8, 28) gives an output signal which controls the load regulator (24, 23) in a direction to increase the field current for the motor which is rotating too fast, while at the same time the limitation of the load regulator (24, 23) is altered (the dotted curve in the symbol instead of the unbroken curve) in such a way that a field increase is permitted. The control magnitude from the amplifier 28 of the slipping regulator then strongly dominates over the magnitude from the amplifier 26, since the amplifier 28 has relatively strong amplification.

FIG. 4 shows in detail a minimum selector 5 intended to select the smallest of two negative voltages as absolute value, and which comprises the diodes d and d and also the resistor R. If the voltages U U which are connected to the anodes of the two diodes d and d2 are different in size, the output signal U will be approximately the same size as the smallest in quantity of the voltages U and U In FIGS. 2 and 3 the number of driving motors con-- nectedin parallel is two. An expert can without difficulty modify the drawings shown to suit a greater number of motors connected in parallel.

The embodiments shown are only example of a driving means according to the invention and the idea of the invention can be realized in many other ways.

For example, instead of said lowest value picked out by a minimum selector, a value can be used which is an expression for theabsolute speed of the vehicle driven by the traction means. Such a value can be obtained, for example by means of a speed measuring radar device utilizing the Doppler-effect.

FIGS. 2a and 2b show details of FIG. 2 and FIGS. 3a and 3b details of FIG. 3. The frames 34 and 35 show each a combination of a device 16 and a device 8 and the frame 36 shows a combination of the devices 7 and 15. Further the frame 33 shows a combination of a device 23 and a device 24.

In FIGS. 2b and 3b the components are designated as follows: 1 58 resistors, 59 capacitors, 71 78 rectifiers, 79 82 amplifiers.

A combination of the devices 17 and 14 gives the same picture as that within the frame 34 except that the rectifier shown in 35 is left out. The combinations (21+ 22) and (I2 13) differ from (17 14) only in that they have an extra input terminal connected to the negative terminal of the amplifier through an extra resistor.

We claim:

1. Slip-controlled drive means for traction purposes comprising a plurality of direct current motors (1), means to supply control quantities of current to said motors comprising for each motor a control system including a controlled rectifier (10,10a), a first reference-value transmitter (2,9), to supply a first reference value, a current transducer (3) for the rotor current and a tachometer (4) connected to each motor, a minimum value selector (5) connected to the outputs of the tachometers to select the lowest of their outputs, a second reference-value transmitter (6) to set a predetermined permissible difference between the speed of any motor and the speed value corresponding to the output of said minimum value selector, a summation device (7) connected to the outputs of said second reference-value transmitter and said minimum value selector to produce the sum of said lowest tachometer value and said difference, a plurality of comparison devices (8) each connected to the output of one of said tachometers and to the output of said summation device and including means to produce a positive difference between the output value of each tachometer and said sum, and devices one connected between each such comparison device and the motor whose tachometer is connected thereto responsive to a value of such positive difference above a given value to supply such positive difference to the control system of such motor to reduce the rotor current thereof.

2. Driving means according to claim 1, which includes a maximum value selector (25) connected to the current transducers and including means to select the highest transducer value, a third reference-value transmitter (29) for the permissible difference between the greatest and smallest rotor currents, a subtracting device (27) connected to the outputs of said maximum value selector and said third reference-value transmitter, said subtracting device including means to produce the difference between said highest current transmitter value and said reference-value transmitter value, and means to supply the output of said subtract ing device to said control systems.

3. Driving means according to claim 1, in which said converters (10) deliver rotor current,

4. Driving means according to claim 1, in which said converters (l0) supply excitation current to the field windings of each motor, and in which said first reference-value transmitters are responsive to the field current, and further including a field current transmitter (11) and a comparison device (22) including means to compare the output value of said field current transmitters, and an amplifier connected to each converter and means to supply the output value of said comparison device to said amplifiers to control the converter.

5. Slip-controlled drive means for traction purposes comprising a plurality of direct current motors (1), means to supply control quantities of current to said motors comprising for each motor a control system including a controlled rectifier (10,10a), a first reference-value transmitter (2,9), to supply a first reference value, a current transmitter (3) for the rotor current and a tachometer (4) connected to each motor, a vehicle speed transmitter (5), a second referencevalue transmitter (6) to set a predetermined permissible difference between the pre-determined motor speed of any motor and the speed value corresponding to the output of said minimum value selector, a summation device (7) connected to the outputs of said second reference-value transmitter and said vehicle speed transmitter to produce the sum of said lowest tachometer value and said vehicle speed transmitter output, a

plurality of comparison devices (8) each connected to the output of one of said tachometers and to the output of said summation device and including means to produce a positive difference between the output value of each tachometer and said sum, and devices one connected between each such comparison device and the motor whose tachometer is connected thereto responsive to a value of such positive difference above a given value to supply such positive difference to the control system of such motor to reduce the rotor current thereof. 

1. Slip-controlled drive means for traction purposes comprising a plurality of direct current motors (1), means to supply control quantities of current to said motors comprising for each motor a control system including a controlled rectifier (10,10a), a first reference-value transmitter (2,9), to supply a first reference value, a current transducer (3) for the rotor current and a tachometer (4) connected to each motor, a minimum value selector (5) connected to the outputs of the tachometers to select the lowest of their outputs, a second reference-value transmitter (6) to set a predetermined permissible difference between the speed of any motor and the speed value corresponding to the output of said minimum value selector, a summation device (7) connected to the outputs of said second reference-value transmitter and said minimum value selector to produce the sum of said lowest tachometer value and said difference, a plurality of comparison devices (8) each connected to the output of one of said tachometers and to the output of said summation device and including means to produce a positive difference between the output vaLue of each tachometer and said sum, and devices one connected between each such comparison device and the motor whose tachometer is connected thereto responsive to a value of such positive difference above a given value to supply such positive difference to the control system of such motor to reduce the rotor current thereof.
 2. Driving means according to claim 1, which includes a maximum value selector (25) connected to the current transducers and including means to select the highest transducer value, a third reference-value transmitter (29) for the permissible difference between the greatest and smallest rotor currents, a subtracting device (27) connected to the outputs of said maximum value selector and said third reference-value transmitter, said subtracting device including means to produce the difference between said highest current transmitter value and said reference-value transmitter value, and means to supply the output of said subtracting device to said control systems.
 3. Driving means according to claim 1, in which said converters (10) deliver rotor current.
 4. Driving means according to claim 1, in which said converters (10) supply excitation current to the field windings of each motor, and in which said first reference-value transmitters are responsive to the field current, and further including a field current transmitter (11) and a comparison device (22) including means to compare the output value of said field current transmitters, and an amplifier connected to each converter and means to supply the output value of said comparison device to said amplifiers to control the converter.
 5. Slip-controlled drive means for traction purposes comprising a plurality of direct current motors (1), means to supply control quantities of current to said motors comprising for each motor a control system including a controlled rectifier (10,10a), a first reference-value transmitter (2,9), to supply a first reference value, a current transmitter (3) for the rotor current and a tachometer (4) connected to each motor, a vehicle speed transmitter (5), a second reference-value transmitter (6) to set a predetermined permissible difference between the pre-determined motor speed of any motor and the speed value corresponding to the output of said minimum value selector, a summation device (7) connected to the outputs of said second reference-value transmitter and said vehicle speed transmitter to produce the sum of said lowest tachometer value and said vehicle speed transmitter output, a plurality of comparison devices (8) each connected to the output of one of said tachometers and to the output of said summation device and including means to produce a positive difference between the output value of each tachometer and said sum, and devices one connected between each such comparison device and the motor whose tachometer is connected thereto responsive to a value of such positive difference above a given value to supply such positive difference to the control system of such motor to reduce the rotor current thereof. 